The present invention relates to a semiconductor device, which uses a carbon-containing layer, such as a fluorine-containing carbon film, as an insulating film, and a method of manufacturing the same.
In order to achieve the high-density integration of semiconductor integrated circuits, it has been developed to scale down patterns, such as wiring, and to multilayer circuits. As one of such developments, there is a multi-layer metallization technique for constructing multi-layer wiring. In this multi-layer metallization technique, upper and lower wiring layers are connected to each other by a conductive part which is arranged in a predetermined region, and an interlayer dielectric film of an insulating material is arranged to separate the wiring layers from each other in a region other than the conductive part.
Typical materials of the interlayer dielectric films include silicon oxide (SiO2). In recent years, in order to more accelerate the operation of integrated circuits, it has been required to lower the relative dielectric constant of the interlayer dielectric films. That is, the relative dielectric constant xcex5 of SiO2 is about 4, and materials having a lower relative dielectric constant than that of SiO2 have been diligently developed.
As an example of a material having a lower relative dielectric constant than that of SiO2, there is a fluorine-containing carbon film comprising carbon and fluorine. This fluorine-containing carbon film can be formed by, e.g., a plasma deposition process using the electron cyclotron resonance (ECR). This method will be described below.
In a deposition system shown in FIG. 10, a microwave of 2.45 GHz is first supplied into a plasma producing chamber 801a from a high-frequency power supply part 802 via a waveguide 802a. At this time, a magnetic field of 875 gausses is applied by magnetic coils 803 and 803a, and Ar gas introduced from an introducing pipe 804 is activated as a high-density plasma by the electron cyclotron resonance.
On the other hand, C4F8 gas and C2H4 gas are introduced into a deposition chamber 801b from a gas supply part 805 via gas introducing pipes 805a and 805b to be activated by the high-density plasma to form active-species. By the active-species, a fluorine-containing carbon film 808 having good adhesion and high hardness is formed on the surface of a wafer 807 which is arranged on a supporting table 806 in the deposition chamber 801b. The wafer 807 is fixed by an electrostatic chuck 806a on the supporting table 806. The interior of the deposition chamber 801b is evacuated to a predetermined degree of vacuum by an evacuating means (not shown) which is communicated with the deposition chamber 801b via an exhaust pipe 810.
By the foregoing, the fluorine-containing carbon film can be formed. However, in order to use the fluorine-containing carbon film as an interlayer dielectric film, it is required to carry out a fine patterning process, such as the formation of a hole portion for arranging a connecting portion for connecting upper and lower wiring layers to each other.
The fine patterning process of the fluorine-containing carbon film will be described below. First, as shown in FIG. 11(a), a fluorine-containing carbon film 902 is formed on a lower wiring layer 901 serving as a substrate as described above. On the fluorine-containing carbon film 902, an inorganic film 903 of SiO2 is formed. Then, as shown in FIG. 11(b), a resist pattern 904 having an opening 904a at a predetermined place is formed on the inorganic film 903 by a well-known photolithography technique.
The resist pattern 904 is then used as a mask to selectively etch the inorganic film 903. Thus, as shown in FIG. 11(c), a hard mask 905 having an opening 905a at a position corresponding to the opening 904a is formed. This etching may be, e.g., a dry etching with the plasma of CF4.
The hard mask 905 is then used as a mask to selectively etch the fluorine-containing carbon film 902. Thus, as shown in FIG. 11(d), a hole portion 906 is formed in the fluorine-containing carbon film 902. This etching may be, e.g., a dry etching with the plasma of oxygen gas. If oxygen gas is used, the etch-selectivity (the ratio of etch rates) between the fluorine-containing carbon film 902 and the hard mask 905 can be great. If the plasma of oxygen gas is used, the resist pattern 904 can be simultaneously removed.
The fine patterning process of the fluorine-containing carbon film using the hard mask will be described below.
In the fine patterning process, a resist pattern formed by the photolithography technique is generally used as a mask to selectively etch. At this time, the resist pattern must have an etching resistance as a mask for an underlying layer to be processed. When the layer to be processed is thick, the resist pattern must particularly have the etching resistance. This resist pattern is formed by, e.g., exposing and developing a photoresist having photosensitivity, and made of an organic material.
However, when an organic film, such as the above described fluorine-containing carbon film, is fine-patterned, the dry etching with the plasma of oxygen is used. In this case, if a resist pattern of an organic film is used as a mask, the resist pattern is also etched, so that it is not possible to carry out a selective etching.
On the other hand, if a master pattern of an inorganic material, such as SiO2, is used when the fluorine-containing carbon film is etched with the plasma of oxygen gas, the master pattern is hardly etched with the plasma of oxygen, so that it is possible to carry out a selective etching For that reason, as described above, a hard mask of SiO2 or the like is used for fine-patterning the fluorine-containing carbon film.
By the way, in order to form this hard mask, an inorganic film of SiO2 or the like is patterned. This patterning may use a dry etching with the plasma of CF4 or C4F8. In this case, since the resist pattern of the organic film is hardly etched, the resist pattern can be used as a mask to carry out the selective etching to form the hard mask as described above.
However, if a hard mask of SiO2 or silicon nitride (SiN), which are generally used for patterning organic films, is used for fine-patterning the fluorine-containing carbon film, there are the following problems, so that the reliability of semiconductor devices using a fluorine-containing carbon film as an interlayer film is deteriorated.
First, since SiO2 and SiN have low adhesion to the fluorine-containing carbon film which is a fluorine-containing organic film, there is a problem in that the hard mask is easily peeled off. As described above, since the hard mask is made of the insulating material, the hold mask is used as a part of an interlayer dielectric film. However, after the fluorine-containing carbon film serving as the interlayer dielectric film is fine-patterned, if a stress in applied in the subsequent process such as forming a metal film for a wiring electrode thereon, the hard mask is sometimes peeled off. If the metal film for the wiring electrode is intended to be flattened by the chemical mechanical polishing method after the metal film is formed, a great stress is applied thereto, so that the hard mask is substantially surely peeled off from the fluorine-containing carbon film.
Next, if the hard mask of SiO2 or SiN is used for fine-patterning the fluorine-containing carbon film, there is a problem in that the etch-selectivity is lowered as follows, As described above, the dry etching with the plasma of oxygen gas is used for fine-patterning the fluorine-containing carbon film. In view of only this point, a high etch-selectivity should be obtained it the hard mask is made of SiO2 or SiN.
However, when the fluorine-containing carbon film is etched with the plasma of oxygen gas, the fluorine-containing carbon film is decomposed to produce F (fluorine) and C (carbon) in atmosphere, and the active-species of F and C are produced by plasma. As a result, since SiO2 or SiN is etched with the active-species, there is a problem in that if the conventional hard mask, together with the fluorine-containing carbon film, is etched, the etch-selectivity is lowered to deteriorate processing precision.
From the point of view of the acceleration of semiconductor devices, it is desired that the insulating film used as the hard mask is made of a material having a lower relative dielectric constant similar to the insulating film of the fluorine-containing carbon film.
The present invention has been made in order to eliminate the above described problems. That is, it is an object of the present invention to improve the reliability of a semiconductor device, which has a carbon-containing insulating film, such as a fluorine-containing carbon film, while considering the acceleration of the same.
In order to accomplish this object, according to one aspect of the present invention, a semiconductor device is provided, the device comprising: a semiconductor substrate, on which an active region is formed; a plurality of wiring layers which are formed on the semiconductor substrate; a first insulating layer containing carbon, the first insulating layer being formed at least between any adjacent two of the wiring layers; and a second insulating layer comprising silicon, carbon and nitrogen, the second insulating layer being formed on the first insulating layer.
With this construction, the first insulating layer containing carbon contacts the second insulating layer comprising silicon, carbon and nitrogen, so that the adhesion between the first and second insulating layers is improved to inhibit peeling. The second insulating layer comprising silicon, carbon and nitrogen can have a higher etch-selectivity than those of conventional layers, and can have a lower dielectric constant than that of an insulating layer comprising silicon and nitrogen or an insulating layer comprising silicon and carbon. Therefore, it is possible to improve the reliability of the semiconductor device while considering the acceleration of the same.
In such a semiconductor device, the second insulating layer preferably further comprises boron in order to lower the relative dielectric constant of the second insulating layer.
An adhesion layer comprising a high-melting point metal and a nitride thereof may be provided in the interface between the first insulating layer and the wiring layers.
According to another aspect of the present invention, a method of manufacturing a semiconductor device is provided, the method comprising the steps of: forming a wiring layer on a semiconductor substrate, on which an active region is formed; forming a first insulating layer containing carbon on the wiring layer; forming a second insulating layer comprising silicon, carbon and nitrogen on the first insulating layer; selectively etching the second insulating layer until the surface of the first insulating layer is partially exposed, selectively etching the first insulating layer using the selectively-etched, second insulating layer, as a mask; and forming a new wiring layer on the second insulating layer after selectively etching the first insulating layer.
With this construction, it is possible to obtain a semiconductor device wherein the first insulating layer containing carbon contacts the second insulating layer comprising silicon, carbon and nitrogen, between the wiring layers. Thus, the adhesion between the first and second insulating layers is improved to inhibit peeling. The second insulating layer comprising silicon, carbon and nitrogen, can have a higher etch-selectivity than those of conventional layers, and can have a lower dielectric constant than that of an insulating layer comprising silicon and nitrogen or an insulating layer comprising silicon and carbon. Therefore, it is possible to improve the reliability of the semiconductor device while considering the acceleration of the same.
This producing method preferably further comprises a step of adding boron to the second insulating layer in order to lower the relative dielectric constant of the second insulating layer.
The step of selectively etching the second insulating layer may be carried out with the plasma of the gas of a compound containing carbon and fluorine or with the plasma of the gas of a compound containing carbon and hydrogen.
If the step of selectively etching the first insulating layer is carried out with the plasma of an oxygen-containing gas, the second insulating layer and the wiring layers are hardly etched.
If the step of selectively etching the first insulating layer is carried out with the plasma of a hydrogen-containing gas, the step is controlled by the etching with reactive ions, so that it is possible to carry out a higher anisotropic etching.